Do I need more researchers or more labs to decrease the research time in the Academy in Anno 2070? Is there some kind of chart which indicates how many of each are required to decrease research time by x unit?
The most important factor is to make sure that your Academies have adequate researcher population nearby them. One lab surrounded by techies is as valuable as 2-3 with only partial coverage. After that, build another research lab with more techies. There isn't a chart because the efficiency varies so significantly between labs based on nearby population.
While I can't source this as its just personal experience, the way it works appears to be linear: One lab working at 100 percent takes twice as long as two labs working at 100 percent, which takes the same time as 3 labs working at ~60-70 percent.